The songs of the mid-twentieth century revival are too sentimental to pass as the real thing. Sentimentality is for people with time on their hands. Sentimentality is for aesthetes. Real folk-songs were written by and for people in the grip of economic necessity. They wanted tabloid banner headlines. They wanted to fill their precious down-time with hard, bright emotion. Real folk-song doesn't hang around and mope. It gives us what we really want- fucking and fighting and unquiet graves.
"Where have all the flowers gone?" If you spend your time soldiering or farming or thieving or minding a power loom you don't need to ask that question. You know where all the fucking flowers have gone. No-one picks flowers promiscuously in real folk-song. You pluck a rose and it's a magical act. Out steps Tam Lin and bang goes your maidenhood and the Queen of Faery has got you on her list.
In folk song the weather is always one thing or the other. There's no Celtic twilight, just bright, shiny morning or mirk, mirk night.